Most computer user interface display concepts are created by artists using image drawing or design applications, such as Microsoft Visio® or Adobe Photoshop®. The resulting concepts are typically passed on to software developers as digital mockup images, such as JPEG files, bitmap files, etc. The developers typically use the concepts to create actual user interfaces using user interface designers, such as Microsoft's Visual Studio®. As used herein, a user interface is code that can produce a visual display of a type that can allow interaction with a user, such as a Web page, a dialog, etc. User interfaces typically include features, such as links, buttons, etc., that facilitate such interaction. Developers typically try to produce an actual user interface that is as close to the concept as possible by comparing the user interface designer's representation of the user interface to a representation of the mockup image in the form of a paper printout or an on-screen display that is separate from the user interface representation.